1. Technical Field of the Invention
The present invention relates generally to an improvement on a gas sensor which is employed, for example, in an oxygen measuring device of an air-fuel ratio control system to measure an oxygen content in exhaust gasses of an internal combustion engine for automotive vehicles, and more particularly to an improved structure of such a gas sensor which provides for ease of installation of an insulation porcelain.
2. Background Art
It is known in the art that burning control of fuel in internal combustion engines based on an oxygen content in exhaust gasses as a parameter indicating an air-fuel ratio is effective in energy saving and emission control. As gas sensors measuring the concentration of oxygen in exhaust gasses, gas sensors equipped with a sensing element made of a solid electrolyte such as zirconia are known.
FIG. 25 shows one example of conventional gas sensors.
The gas sensor 9 consists of a sensing element 910, a housing 94, and a protective cover 92. The sensing element 910 has a portion 911 exposed to a gas to be measured and is retained within the housing 94. The protective cover 92 is installed on the housing 94 and surrounds the gas-exposed portion 911 of the sensing element 910. A packing or sealing member 918 is disposed between the housing 94 and the sensing element 910.
The sensing element 910 is of a cup-shape and has defined therein a reference gas chamber 912 leading to the atmosphere. A gas chamber 913 into which the gas to be measured is admitted is defined in the protective cover 92 around the sensing element 910. The sensing element 910 has a reference electrode exposed to the reference gas chamber 912 and a measuring electrode exposed to the gas chamber 913. The sensing element 910 also has a heater 915 disposed therein.
The sensing element 910 is electrically connected to leads 981 and 991 through coupling terminals 982 and 992 and metallic terminals 983 and 993, respectively. The metallic terminals 983 and 993 are in contact with terminals formed on the sensing element 910 leading to the reference and measuring electrodes, respectively. A lead 971 is connected to the heater 915 for supplying the power thereto.
Bases of the leads 981 and 991 connected to the coupling terminals 982 and 992 are retained within an insulation porcelain 95. The insulation porcelain 95 is held by an inner cover 931 and an outer cover 932 of an air cover assembly. Specifically, the inner cover 931 supports at an end thereof a lower portion of the insulation porcelain 95, while the outer cover 932 presses at a shoulder thereof the insulation porcelain 95 downward against the end of the inner cover 931. A disc spring 956 is disposed between the shoulder of the outer cover 932 and the insulation porcelain 95.
An air cover 933 surrounds an upper portion of the outer cover 932 through a cylindrical water-repellent filter 938 An elastic insulator 945 is fitted within an open end portion of the air cover 933 which holds the leads 971, 981, and 991 therein.
The air cover 933 and the outer cover 932 have first air vents 936 and second air vents 937, respectively, which lead to the reference gas chamber 912 through the water-repellent filter 938 for inducting the air into the reference gas chamber 912.
The elastic insulator 945, the outer cover 932 of the air cover assembly, and the air cover 933 are joined together by crimping.
The gas sensor 9 produces at the sensing element 910 an electromotive force as a function of a difference in concentration between the air in the reference gas chamber 912 and the gas in the gas chamber 913 to be measured and outputs it through the leads 981 and 991.
The above described structure of the gas sensor 9 contributes to the improvement of control ability in automotive internal combustion engines, however, it is being still required for decreasing the overall size and manufacturing costs, and improving the durability of the gas sensor 9.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of a gas sensor which is compact in size, but possesses high durability and may be manufactured at low costs.
According to one aspect of the invention, there is provided an improved structure of a gas sensor designed to measure a given component content in a gas. The gas sensor comprises: (a) a housing having a first end and a second end; (b) a sensing element disposed in the housing, the sensing element having a base portion and a gas-sensing portion, the base portion projecting from the first end of the housing, the gas-sensing portion projecting from the second end of the housing; (c) a first cover installed on the first end of the housing to cover the base portion of the sensing element; (d) a plurality of electric terminals connected to the sensing element for establishing electric communication between the sensing element and an external device; (e) an insulator in which the electric terminals are disposed, the insulator including a body and a flange, the flange having an groove formed in a peripheral wall thereof; (f) a second cover installed on the second end of the housing to cover the gas-sensing portion of the sensing element and retain the insulator therein, the second cover including a small-diameter portion, a large-diameter portion, and a shoulder connecting between the small-diameter portion and the large-diameter portion, the small-diameter portion being greater in diameter than the body of the insulator and smaller in diameter than the flange of the insulator, the large-diameter portion being greater in diameter than the flange of the insulator; and (g) an elastic holding mechanism disposed between the groove of the flange of the insulator and an inner wall of the large-diameter portion of the second cover to be deformable elastically in a radius direction of the second cover to hold the insulator within the second cover firmly.
In the preferred mode of the invention, the elastic holding mechanism includes a plurality of springs disposed in the groove of the flange at regular intervals away from each other.
Each of the springs is made of a corrugated plate which is disposed between the groove of the flange and the inner wall of the large-diameter portion of the second cover so as to urge the flange of the insulator elastically inwardly of the second cover, thereby holding the insulator within the second cover.
Each of the corrugated plate may have an extension wall which is placed in surface contact with the inner wall of the second cover and welded at a portion thereof to the inner wall of the second cover.
The elastic holding mechanism may alternatively be made of a spring ring disposed in the groove of the flange of the insulator.
The spring ring has disposed on a periphery wall thereof a plurality of members which are so folded as to produce elastic pressure between the flange of the insulator and the inner wall of the second cover for holding the insulator within the second cover firmly.
According to the second aspect of the invention, there is provided a gas sensor measuring a given component content in a gas which comprises: (a) a housing having a first end and a second end; (b) a sensing element disposed in the housing, the sensing element having a base portion and a gas-sensing portion, the base portion projecting from the first end of the housing, the gas-sensing portion projecting from the second end of the housing; (c) a first cover installed on the first end of the housing to cover the base portion of the sensing element; (d) a plurality of electric terminals connected to the sensing element for establishing electric communication between the sensing element and an external device; (e) an insulator in which the electric terminals are disposed, the insulator including a body and a flange; (f) a second cover installed on the second end of the housing to cover the gas-sensing portion of the sensing element and retain the insulator therein, the second cover including a small-diameter portion, a large-diameter portion, and a shoulder connecting between the small-diameter portion and the large-diameter portion, the small-diameter portion being greater in diameter than the body of the insulator and smaller in diameter than the flange of the insulator, the large-diameter portion being greater in diameter than the flange of the insulator; and (g) an elastic holding mechanism disposed in a gap between the insulator and an inner wall of the second cover so as to produce elastic pressure which holds the insulator elastically within the second cover.
In the preferred mode of the invention, the elastic holding mechanism is disposed in the gap between the body of the insulator and an inner wall of the large-diameter portion of the second cover in contact with the body of the insulator and the inner wall of the large-diameter portion of the second cover to urge the flange elastically into constant engagement with an inner wall of the shoulder of the second cover, thereby retaining the insulator within the second cover firmly.
The elastic holding mechanism is made of a ring base and a plurality of elastic deformable members installed on the ring base. Each of the elastic deformable members is placed in contact with the body of the insulator and the inner wall of the large-diameter portion of the second cover to urge the flange elastically into constant engagement with an inner wall of the shoulder of the second cover, thereby retaining the insulator within the second cover firmly.
The elastic holding mechanism may alternatively include a base and an elastically deformable member. The base is placed in contact with one of opposed surfaces of the flange of the insulator remote from an inner wall of the shoulder of the second cover. The elastically deformable member is press fit within the gap between the flange of the insulator and the inner wall of the large-diameter portion of the second cover in surface contact with the inner wall of the large-diameter portion of the second cover to urge the flange inwardly in the radius direction of the second cover elastically, thereby retaining the insulator within the second cover firmly.
The elastic holding mechanism may alternatively include a ring base and an elastically deformable member installed on the ring base. The ring base is placed in contact with one of the opposed surfaces of the flange of the insulator remote from the inner wall of the shoulder of the second cover. The elastically deformable member is press fit within the gap between the flange of the insulator and the inner wall of the large-diameter portion of the second cover to urge the flange inwardly in the radius direction of the second cover elastically, thereby retaining the insulator within the second.
The elastically deformable member may have a V-shape or a U-shape.
The elastic holding mechanism may alternatively include a ring base and a plurality of elastically deformable members installed on the ring. The ring base is placed in contact with one of the opposed surfaces of the flange of the insulator remote from the inner wall of the shoulder of the second cover. The elastically deformable members is press fit within the gap between the flange of the insulator and the inner wall of the large-diameter portion of the second cover to urge the flange inwardly in a radius direction of the second cover elastically, thereby retaining the insulator within the second cover firmly.
The elastic holding mechanism may alternatively include a base and an elastically deformable member extending from the base. The base is placed between the inner wall of the shoulder of the second over and the surface of the flange of the insulator. The elastically deformable member is press fit within the gap between the flange of the insulator and the inner wall of the large-diameter portion of the second cover to urge the flange inwardly in the radius direction of the second cover elastically, thereby retaining the insulator within the second cover firmly.
The elastically deformable member may be made of a corrugated spring plate extending longitudinally of the insulator in contact with the flange of the insulator and the inner wall of the large-diameter portion of the second cover.
The base of the elastic holding mechanism may be made of a ring. The corrugated spring plate is of an annular shape and extends from a periphery of the ring.
The elastic holding mechanism may alternatively include a ring base and elastically deformable corrugated members connected to the ring base. The ring base is placed between the inner wall of the shoulder of the second over and the surface of the flange of the insulator. Each of the elastically deformable corrugated members is press fit within the gap between the flange of the insulator and the inner wall of the large-diameter portion of the second cover to urge the flange inwardly in the radius direction of the second cover elastically, thereby retaining the insulator within the second cover firmly.
The elastic holding mechanism may alternatively include a protrusion provided on an inner wall of the large-diameter portion of the second cover and an elastically deformable member disposed between the protrusion and the surface of the flange of the insulator to urge the flange elastically into constant engagement with the shoulder of the second cover, thereby retaining the insulator within the second cover firmly.
The protrusion is made of a ring connected to the inner wall of the large-diameter portion of the second cover. The elastically deformable member is made of an annular spring which is substantially of S-shape in cross section.
The elastic holding mechanism may alternatively include a plurality of corrugated spring plates and a ridge formed on the inner wall of the large-diameter portion of the second cover on which the flange of the insulator is placed. The corrugated spring plates are disposed in the gap between the inner wall of the shoulder of the second cover and one of the opposed surfaces of the flange to produce elastic pressure which urges the flange elastically against the ridge, thereby holding the insulator within the second over firmly.
The elastic holding mechanism may alternatively include a spring ring having a corrugated shape in cross section and a ridge formed on the inner wall of the large-diameter portion of the second cover on which the flange of the insulator is placed. The spring ring is disposed in the gap between an inner wall of the shoulder of the second cover and one of the opposed surfaces of the flange to produce elastic pressure which urges the flange elastically against the ridge, thereby holding the insulator within the second over firmly.
The elastic holding mechanism may alternatively include a plurality of springs each made up of an outer plate, an inner plate, and a base connecting between the outer and inner plates. The outer plate is in elastic contact with the inner wall of the large-diameter portion of the second over. The inner plate is in elastic contact with an outer wall of the body of the insulator, thereby bringing the base into constant engagement with one of the opposed surfaces of the flange of the insulator to urge the flange elastically against an inner wall of the shoulder of the second cover.
The outer plate may have an extension wall which is placed in surface contact with the inner wall of the second cover and welded at a portion thereof to the inner wall of the second cover.
The elastically deformable member of the elastic holding mechanism may have an extension wall which is placed in surface contact with the inner wall of the second cover and welded at a portion thereof to the inner wall of the second cover.
The elastic holding mechanism may alternatively be made of a spring plate having a first and a second end. The first end is connected to an inner wall of the large-diameter portion of the second cover. The second end is in elastic contact with one of opposed surfaces of the flange of the insulator, thereby urging the flange of the insulator into constant engagement of the other opposed surface of the flange with an inner wall of the shoulder of the second cover.
According to the third aspect of the invention, there is provided a gas sensor measuring a given component content in a gas which comprises: (a) a housing having a first end and a second end; (b) a sensing element disposed in the housing, the sensing element having a base portion and a gas-sensing portion, the base portion projecting from the first end of the housing, the gas-sensing portion projecting from the second end of the housing; (c) a first cover installed on the first end of the housing to cover the base portion of the sensing element; (d) a plurality of electric terminals connected to the sensing element for establishing electric communication between the sensing element and an external device; (e) an insulator in which the electric terminals are disposed, the insulator including a body and a flange; (f) a second cover installed on the second end of the housing to cover the gas-sensing portion of the sensing element and retain the insulator therein, the second cover including a small-diameter portion, a large-diameter portion, and a shoulder connecting between the small-diameter portion and the large-diameter portion, the small-diameter portion being greater in diameter than the body of the insulator and smaller in diameter than the flange of the insulator, the large-diameter portion being greater in diameter than the flange of the insulator; and (g) a holding mechanism disposed between an end of the body of the insulator and the first end of the housing to retain the insulator within the second cover.
In the preferred mode of the invention, the holding mechanism is made of a spring.
The holding mechanism may alternatively be made of a cylindrical rigid member.
According to the fourth aspect of the invention, there is provided a gas sensor measuring a given component content in a gas which comprises: (a) a housing having a first end and a second end; (b) a sensing element disposed in the housing, the sensing element having a base portion and a gas-sensing portion, the base portion projecting from the first end of the housing, the gas-sensing portion projecting from the second end of the housing; (c) a first cover installed on the first end of the housing to cover the base portion of the sensing element; (d) a plurality of electric terminals connected to the sensing element for establishing electric communication between the sensing element and an external device; (e) an insulator in which the electric terminals are disposed, the insulator including a body and a flange; (f) a second cover installed on the second end of the housing to cover the gas-sensing portion of the sensing element and retain the insulator therein, the second cover including a small-diameter portion, a large-diameter portion, and a shoulder connecting between the small-diameter portion and the large-diameter portion, the small-diameter portion being greater in diameter than the body of the insulator and smaller in diameter than the flange of the insulator, the large-diameter portion being greater in diameter than the flange of the insulator; and (g) a holding member holding the insulator within the second cover, the holding member being made of a wedge-shaped member and fitted between the flange of the insulator and an inner wall of the large-diameter portion of the second cover to retain the insulator firmly.